1. Field of the Invention
The present invention relates to a photoresist monomer, polymers derived from the monomer, and photoresist compositions comprising the same. More specifically, the invention relates to a bis(norbornene carboxylate) and a bis(norbornene dicarboxylate) monomers comprising an acetal group, polymers derived from the same, and photoresist compositions comprising the same.
2. Description of the Background Art
Recently, chemical amplification type DUV photoresists have been investigated in order to achieve high sensitivity in minute image formation processes for preparing semiconductor devices. Such photoresists are prepared by blending a photoacid generator and matrix resin polymer having an acid labile group.
In the lithography process, resolution depends upon the wavelength of the light sourcexe2x80x94the shorter the wavelength, the more minute pattern can be formed.
Recently, chemical amplification type DUV photoresists have been investigated for achieving a high sensitivity in minute image formation processes for preparing semiconductor devices. Such photoresists are typically prepared by blending a photoacid generator and a matrix resin polymer having an acid labile group. The resolution of a lithography process depends, among others, on the wavelength of the light source, i.e., shorter the wavelength, smaller the pattern formation.
In general, a useful photoresist (hereinafter, abbreviated to as xe2x80x9cPRxe2x80x9d) has a variety of desired characteristics, such as an excellent etching resistance, heat resistance and adhesiveness. Moreover, the photoresist should be easily developable in a readily available developing solution, such as 2.38% aqueous tetramethylammonium hydroxide (TMAH) solution. However, it is very difficult to synthesize a photoresist polymer, especially DUV photoresist, which meets all of these desired characteristics. For example, a polymer having a polyacrylate polymer backbone are readily available, but it has a poor etching resistance and is difficult to develop. In order to increase its etching resistance, several groups have added an alicyclic unit to the polymer backbone. However, photoresist copolymers comprising entirely of an alicyclic polymer backbone is difficult to form.
To solve some of the problems described above, Bell Research Center developed a polymer having the following chemical formula: 
where the polymer backbone is substituted with a norbornene, an acrylate and a maleic anhydride unit. Unfortunately, even in the unexposed regions, the maleic anhydride moiety (xe2x80x98Axe2x80x99 portion) dissolves readily in 2.38 wt % aqueous TMAH solution. Therefore, in order to inhibit the dissolution of the polymer in the unexposed section, the ratio of xe2x80x98Yxe2x80x99 portion having tert-butyl substituent must be increased, but this increase results in a relative decrease in the xe2x80x98Zxe2x80x99 portion, which is responsible for the adhesiveness of the photoresist polymer. This decrease in the relative amount of the xe2x80x98Zxe2x80x99 portion may result in separation of the photoresist from the substrate during a pattern formation.
In order to solve this problem, cholesterol type dissolution inhibitors have been added to the polymer to form a two-component system. However, since the amount of the dissolution inhibitor is very high [about 30% (w/w) of the resin], reproducibility is low and the production cost is high, thereby making the system unsuitable as a PR.
Therefore, there is a need for a photoresist polymer which provides an excellent etching properties, adhesiveness, ease of development, and good pattern formation.
An object of the present invention is to provide PR polymers having excellent etching resistance, adhesiveness and photosensitivity, and a process for preparing the same.
Specifically, the present invention provides novel PR monomers, in particular, bis(norbornene carboxylate) and bis(norbornene dicarboxylate) compounds, which comprise an acetal protecting group and a process for preparing the same.
Another object of the present invention is to provide photoresist compositions comprising the PR polymers described above, and a process for preparing the same.
Still another object of the present invention is to provide a semiconductor device produced by using the PR composition.
The present invention provides photoresist monomers of the formula: 
where A is hydrogen or xe2x80x94COOR1; Axe2x80x2 is hydrogen or xe2x80x94COOR2; each of R1 and R2 is independently hydrogen or, substituted or non-substituted (C1-C10) linear of branched alkyl, cycloalkyl, alkoxyalkyl or cycloalkoxyalkyl; X is substituted or non-substituted (C1-C10) linear of branched alkyl, cycloalkyl, alkoxyalkyl or cycloalkoxyalkyl; m is an integer from 1 to 8; and n is an integer from 1 to 3. In the present invention, the compound of formula 1 is named using the following nomenclature: the bis(norbornene carboxylate) group is named first as bis(norbornene carboxylyl) followed by the group containing xe2x80x94Oxe2x80x94(X)mxe2x80x94Oxe2x80x94 as a dihydroxy group which is followed by the name diethyl ether. For example, a compound of formula 1 where A=H, m=1, n=1 and X=propyl would be called bis(5-norbornene-2-carboxylyl)-1,3-propanediol diethyl ether.
Thus, the compound of Formula 1 encompasses bis(norbornene carboxylate) of formula 1a and bis(norbornene dicarboxylate) of formula 1b: 
Preferably, R1 and R2 are selected from the group consisting of hydrogen, methyl, ethyl and tert-butyl. More preferably, R1 and R2 are identical.
The following are particularly preferred compounds of formula 1: 
The compound of formula 1 can be prepared by reacting a compound of Formula 5: 
with a compound of Formula 6: 
preferably in an organic solvent, in the presence of an acid catalyst, where A, X, m and n are those defined above. The reaction temperature is typically in the range of from about 10xc2x0 C. to about 50xc2x0 C. And the reaction time is generally from about 8 to about 12 hours. After the reaction, removal of the organic solvent typically affords the desired compound of formula 1.
While any non-protic organic solvent can be used in the preparation of compound of formula 1, typically tetrahydrofuran (THF), dimethylformamide, dioxane, benzene, toluene or xylene are used. In addition, it is within the knowledge of one skilled in the art of organic chemistry in selecting an appropriate acid catalyst for the above described method. Such acid catalyst includes any organic and inorganic acids. A preferred acid catalyst includes para-toluenesulfonic acid.
The compound of formula 5 is preferable selected from the group consisting of 5-norbornene-2-carboxylic acid and 5-norbornene-2,3-dicarboxylic acid. And preferably, a compound of formula 6 is selected from a group consisting of 1,4-butanediol divinyl ether, 1,3-propanediol divinyl ether and 1,4-cyclohexane dimethanol divinyl ether.
The present invention also provides photoresist copolymer comprising a compound of formula 1. As used herein, the term xe2x80x9cphotoresist copolymer comprising a compoundxe2x80x9d of formula 1 means a photoresist copolymer which is derived from polymerizing the compound of formula 1.
The photoresist copolymer of the present invention can also include a second monomer which is represented by a compound of the formula: 
where Y is substituted or non-substituted (C1-C10) linear or branched alkyl, cycloalkyl, alkoxyalkyl or cycloalkoxyalkyl; 1 is an integer from 1 to 8, and s is an integer from 1 to 3. Preferably, the second monomer is selected from the group consisting of 2-hydroxyethyl5-norbornene-2-carboxylate or 3-hydroxypropyl 5-norbornene-2-carboxylate.
In addition, the photoresist copolymer of the present invention can also include a third monomer is selected from the group consisting of a compound of the formula: 
where each of R, R3 and R4 is independently hydrogen or substituted or non-substituted (C1-C10) linear or branched alkyl, cycloalkyl, alkoxyalkyl or cycloalkoxyalkyl; and each of t and u is independently an integer from 1 to 3. Preferably, a compound of formula 8 is tert-butyl-5-norbornene-2-carboxylate or 5-norbornene-2-carboxylic acid. And a preferred compound of formula 9 is 5-norbornene-2,3-dicarboxylic acid.
The photoresist copolymer of the present invention can also include maleic anhydride as a fourth monomer.
Preferably, the molecular weight of the PR copolymer of the present invention is in the range of from about 3000 to about 100,000.
Particularly preferred photoresist copolymers of the present invention includes: poly[bis(5-norbornene-2-carboxylyl)-1,4-butanediol diethyl ether/2-hydroxyethyl-5norbornene-2-carboxylate/tert-butyl-5-norbornene-2-carboxylate/5-norbornene-2-carboxylic acid/maleic anhydride](10): 
Poly[bis(5-norbornene-2-carboxylyl)-1,3-propandioldiethylether/2-hydroxyethyl-5-norbornene-2-carboxylate/tert-butyl-5-norbornene-2-carboxylate/5-norbornene-2-carboxylic acid/maleic anhydride] (11): 
Poly[bis(5-norbornene-2-carboxylyl)-1,4-cyclohexane dimethanol diethylether/2-hydroxyethyl-5-norbornene-2-carboxylate/tert-butyl-5-norbornene-2-carboxylate/5-norbornene-2-carboxlic acid/maleic anhydride] (12): 
Poly[bis(5-norbornene-2,3-dicarboxylyl)-1,4-butanedioldiethyether/2-hydroxyethyl-5-norbornene-2-carboxylate/tert-butyl-5-norbornene-2-carboxylate/maleic anhydride] (13): 
Poly[bis(5-norbornene-2,3-dicarboxylyl)-1,3-propanediol diethyl ether/2-hydroxyethyl-5-norbornene-2-carboxylate/tert-butyl-5-norbornene-2-carboxylate/5-norbornene-2-carboxylic acid/maleic anhydride ] (14): 
Poly[bis(5-norbornene-2,3-dicarboxylyl)-1,4-cyclohexane dimethanol diethyl ether/2-hydroxyethyl-5-norbornene-2-carboxylate/tert-butyl-5-norbornene-2-carboxylate/5-norbornene-2-carboxylic acid/maleic anhydride] (15): 
For the compounds of Formulas 10-15, v, w, x, y and z represents the relative amounts of each monomer, wherein the ratio of v:w:x:y:z=0xcx9c99 mol %:0xcx9c99 mol %:0xcx9c99 mol %:0.1xcx9c99 mol %:0xcx9c99 mol %.
The photoresist copolymer of the present invention can be prepared by radical polymerization of monomers with a typical radical polymerization initiator. For example, a typical polymerization reaction includes (a) admixing, preferably in an organic solvent, (i) a compound of Formula 1 (the first monomer), (ii) a compound of Formula 7 (the second monomer), optionally (iii) more than one compound of Formula 8 and/or 9 (the third monomer), and (iv) maleic anhydride (the fourth monomer); (b) adding a polymerization initiator to the admixture; and (c) polymerizing the admixture obtained from (b) in an inert atmosphere, preferably in a nitrogen or argon atmosphere.
Alternatively, the photoresist copolymer in the present invention can be prepared by reacting the photoresist copolymerxe2x80x94obtained from polymerizing a compound of Formula 7, more than one compound of Formula 8 and/or 9, and maleic anhydridexe2x80x94with a compound of Formula 6 in the presence of an acid catalyst.
In the present invention, polymerization is carried out by either a bulk polymerization or a solution polymerization. A preferred polymerization solvent is selected from the group consisting of cyclohexanone, tetrahydrofuran, dimethylformamide, dimethylsulfoxide, dioxane, methyl ethyl ketone, benzene, toluene and xylene. The polymerization initiator is preferably selected from the conventional radical polymerization initiators, such as benzoylperoxide, 2,2xe2x80x2-azobisisobutyronitrile (AIBN), acetylperoxide, laurylperoxide, tert-butylperacetate, tert-butylhydroperoxide and di-tert-butylperoxide.
As shown above, the photoresist copolymer of the present invention is partially cross-linked. In an exposed region, both the acid labile protecting group and the acetal group are deprotected by the acid that is generated in photolithography. This deprotection results in a large difference in the solubility rate between in the exposed region and the unexposed region, and as a result, decreases top-loss and enhances profile.
The present invention also provides a PR composition comprising the PR copolymer described above, an organic solvent, and a photoacid generator. Preferred photoacid generators include sulfide or onium type compounds. A suitable photoacid generator may be one or more compounds selected from the group consisting of diphenyl iodide hexafluorphosphate, diphenyl iodide hexafluoroarsenate, diphenyl iodide hexafluoroantimonate, diphenyl p-methoxyphenyl triflate, diphenyl p-toluenyl triflate, diphenyl p-isobutylphenyl triflate, diphenyl p-tert-butylphenyl triflate, triphenylsulfonium hexafluoroantimonate, triphenylsulfonium triflate and dibutylnaphthylsulfonium triflate. The photoacid generator is typically used in an amount of from about 0.1% by weight to about 10% by weight of the photoresist copolymer.
Useful organic solvents for the photoresist composition include methyl 3-methoxypropionate, ethyl 3-ethoxypriopionate, propylene glycol methyl ether acetate, cyclohexanone, 2-heptanone, and (2-methoxy)ethyl acetate. Preferably, the amount of organic solvent present in the photoresist composition of the present invention is in the range of from about 200% by weight to about 1000% by weight of the PR copolymer.
The PR composition is typically prepared by dissolving the photoresist copolymer of the present invention in an organic solvent in the amount ranging from about 10% by weight to about 30% by weight of the solvent, blending the photoacid generator with the photoresist copolymer in the amount ranging from about 0.1% by weight to about 10% by weight of the copolymer and then filtering the resulting mixture through a hyperfine filter.
The PR composition of the present invention has an excellent etching resistance, adhesiveness and heat resistance. Also, it has an excellent resolution and profile because it is partially cross-linked. Moreover, the PR composition of the present invention reduces top-loss of the photoresist, and therefor is very useful as an ArF photosensitive film.
The present invention also provides the method for forming the PR pattern comprising the steps of: (a) coating the above described photoresist composition on a substrate of semiconductor element to form a photoresist film; (b) exposing the photoresist film to light using a light source; and (c) developing the photoresist film. Optionally, the photoresist film can be heated (i.e., baked), preferably to temperature in the range of from about 70xc2x0 C. to about 200xc2x0 C., before and/or after the step (b).
Exemplary light sources which are useful for forming the PR pattern include ArF (193 nm), KrF (248 nm), VUV (157 nm), EUV, E-beam, X-ray and ion beam. Preferably, the irradiation energy is in the range of from about 1 mJ/cm2 to about 100 mJ/cm2.
In one particular example, the photoresist pattern formation process of the present invention comprises the steps of: i) forming a thin-film of PR composition by spin coating the photoresist composition of the present invention on a silicon wafer; ii) soft baking the silicon wafer in an oven or on a hot plate at temperature in the range of from about 80xc2x0 C. to about 150xc2x0 C. for 1 to 5 minutes; iii) exposing the silicon wafer to light using an ArF exposer or excimer laser; and iv) baking the exposed wafer at temperature in the range of from about 100xc2x0 C. to about 200xc2x0 C. The exposed silicon wafer is developed by immersing it in a 2.38 wt % TMAH solution for 90 seconds to get hyperfine resist image.
The present invention also provides a semiconductor device, which is manufactured using the photoresist composition described above.